Refigeration apparatus



Aug. 28, 1962 D. G. RICH REFRIGERATION APPARATUS Filed April 25, 1960FIG. I

MA TATA'A'F A A AA A l V H HIH u n if AWAWMV'AV (i III FIG. 3

INVENTOR.

DONALD e. RICH ATTORNEY.

United States Patent Qfifice i atented Aug. 28, 1962 ware Filed Apr. 25,1960, Ser. No. 24,312 4 Claims. ((1 623tl5) This invention relates toair conditioning apparatus and, more particularly to air conditioningapparatus including heat exchangers of the evaporative type.

The basic principle of operation of a heat exchanger involves thepassage of two heat exchange mediums in relationship with each othersuch that heat is transmitted from one of the heat exchange mediums tothe other. By way of example, a condenser in a standard refrigerationsystem may pass compressed refrigerant gas through a series of pipeswhich form a heat exchanger. Air or water may be passed across thesurface of the pipes to remove heat from the compressed gas and condenseit to a liquid. Obviously, a heat exchanger of this type is limited inits capacity by the temperature difference between the internal fluide.g., refrigerant, and the external fluid e.g., air. Another obviouslimitation arises by reason of the fact that the temperature of air orother external heat exchange medium which is passed across the exteriorsurface of the heat exchange pipes rises due to absorption of heat fromthe heat exchanger and as more capacity is required, it is frequentlynecessary to increase the volume of air which is passed by using fans orother means. One of the Well known techniques for increasing thecapacity of a given size heat exchanger is to employ fins on the outsideof the heat exchange tubes to increase the area available for heattransfer. Another method is to employ an evaporative heat exchanger. Inan evaporative heat exchanger a heat exchange medium is flowed acrossthe exterior of the heat exchange pipes. Since a substantial quantity ofheat must be added to any liquid in order to vaporize it, heat may beremoved from the fluid on the interior of the pipes by conductionthrough the pipe walls and be carried away from the heat exchanger byvaporizing the liquid heat exchange medium which is flowed across theexterior of the pipes.

Typical evaporative heat exchangers of prior art construction employspray systems or other means for discharging a quantity of liquid overthe exterior surfaces of a heat exchanger. In order to secure maximumheat transfer capacity, it is desirable to maintain the entire ex teriorsurface of the heat exchange tubes wetted with a thin film of exteriorliquid heat exchange medium such as Water. If substantially the entireexterior surface of the heat exchange tubes is not wetted, dry areaswill be present on the tubes or on the fins where only convective heattransfer may take place and at which the advantages of evaporative heattransfer may not be obtained clue to the lack of liquid available forevaporation. On the other hand, if too great a quantity of liquid isflowed over the surface of the heat exchange tubes, a thick layer ofliquid may be built up on the tubes and fins which Will tend to insulatethe tube and actually inhibit heat transfer.

In a typical heat exchanger construction employing a spray system fordischarging droplets of Water over the exterior surface of a heatexchange tube, the surface tension of the liquid tends to make theliquid coalesce into a numher of discrete droplets on the surface of thetube and fins. The droplets possess the disadvantage of being relativelythick and at the same time, the areas between the droplets tend to bedry. Another disadvantage of a spray system is that if a large number oftubes are disposed vertically beneath the spray, the lower tubes willnot be directly wetted by the spray but depend upon liquid dripping fromthe tubes above. Consequently, the tubes belowmay not be uniformlywetted. In order to overcome this tendency, it is frequent practice tospray a very large excess of liquid over the heat exchange tubes and tocollect the liquid which drips olf the tubes into a sump. This liquid isthen pumped back to the spray system Where it is again discharged overthe surface of the heat exchange tubes. While this system produces morecomplete wetting of the heat exchange tubes, it introduces additionaldisadvantages. For example, the liquid from the spray system tends tobecome entrained in the air surrounding the heat exchanger. If the heatexchanger is employed as a condenser on the top of a low building theentrained moisture from the condenser may find its way to the streetbelow where it is disagreeable to passersby. More serious, however, isthe loss of liquid from the system and the necessity for maintaining anopen sump over the heat exchanger to collect the excess liquid. The opensump involves the additional expense of a pump and other piping must beassociated with it to return the liquid to the spray system.Furthermore, since heat exchangers of this type are frequently locatedon the roof of a building, an open sump tends to collect dust, smoke,soot, insects and other foreign material which must be periodicallyremoved from it in order to prevent fouliug'of the spray system. A layerof algae frequently builds up in an open sump of a conventionalevaporative heat exchanger which can be removed only with greatdifficulty and which tends to foul the pumps and piping in the system.

It is, therefore, desirable to provide some means of maintaining auniformly thin film of liquid on substantially the entire surface of anevaporative heat exchanger without the necessity for employing an opensump or a spray system with their attendant disadvantages.

Accordingly, it is an object of this invention to provide an improvedevaporative heat exchanger.

It is a further object of this invention to provide an improved airconditioner.

It is a still further object of this invention to provide an improvedmethod of making an evaporative heat exchanger.

These objects are achieved in the embodiment shown by providing aplurality of hollow porous metal fins about one or more pipes which forman evaporative heat exchanger. A liquid heat exchange medium such asWater is flowed into the interior of the hollow fins and due to theirporosity is allowed to seep from the interior of the fins to theexterior thereof where it is constantly available for evaporation. 'Bythis means substantially the entire porous exterior surface of thehollow metal fins maybe continually wetted with a thin film of liquidthereby providing maximum capacity for a heat exchanger of this type.

A heat exchanger of the type described may be made by rolling a poroussheet of compacted metal powder and stamping therefrom a plurality oflipped Walls. The lipped walls may then be assembled with alternate lips3 facing each other on a heat exchange tube to form a hollow finned heattransfer surface. Adjacent lips may then be sealed together by furnacebrazing or other appropriate means to form a plurality of hollow finsdisposed about the surface of the heat exchange pipes.

These and other objects of this invention will become apparent byreference to the following specification and attached drawings wherein:

FIGURE 1 is a side view partially broken away showing an evaporativeheat exchanger constructed in accordance With this invention mounted onthe roof of a build- FIGURE 2 is a cross-sectional view takensubstantially on lines II-II of FIGURE 1; and

FIGURE 3 illustrates a method of sealing the lip portions of the wallsof heat exchange fins made in accordance with the described method.

Referring particularly to FIGURE 1, a heat exchanger in accordance withthis invention is shown mounted on supports 18 which may hold the heatexchanger in a slightly tilted position on the roof of a building. Itwill be understood that for purposes of illustration the heat exchangerdescribed is adapted to be employed as an evaporative condenser on theexterior of a building. However, other applications of such a heatexchanger will be readily apparent to those skilled in the art. Forexample, a heat exchanger of the type described is particularly suitedto location within the interior of a building because of the eliminationof a spray system and consequent entrainment problems.

Heat exchanger lt) comprises a plurality of heat exchange tubes or pipes11 having disposed thereon a plurality of fins 12. Fins 12 each comprisea first porous wall 13 and a second porous wall 14 as can best be seenin FIGURE 2. Porous walls 13 and 14 are desirably made of a compactedmetal powder having good thermal conductivity characteristics such ascopper. Walls 13 and 14 may be generally flat sided as shown in FIGURE 2or if desired they may be corrugated. Edge portions 31, 32 and 33 areprovided with lips 15 which are bent out of the plane of walls 13 and 14and which have a narrow flat portion for engagement with a correspondinglip of another wall. For convenience of manufacture, wall 13 ispreferably identical to wall 14 and engagement between corresponding lipportions is secured by reversing alternate walls comprising the fins andpositioning them so that the flat portions of lips 15 are closelyadjacent each other asshown in FIGURE 2. Appropriate holes are formed inwalls 13 and 14 for accommodation of impervious heat exchange pipes 11such as copper which pass therethrough. 7

Each pair of adjacent lips 15 form and are sealed to each other on threeedges 31, 32, and 33 of fin 12. Consequently, fin 12 comprises a hollowenvelope 16 having sealed lip portions and spaced wall portions for theaccommodation of a heat exchange fluidmediurn such as water therein. Theremaining of fourth edge of fins 12 may be left substantially open andcommunicates with a header 17 for the purpose of supplying the heatexchange medium to the interior of the fins. A conduit 19 suppliesliquid to header 1.7. The supply of liquid into header 17 is controlledby a pressure regulating valve 20 and a pump 21. Valve 20 may serve toregulate the pressure of fluid in header 17 and consequently in theinterior of fins 12 if desired. Alternatively, header 17 may comprise astorage tank or the lower portion of a storage tank where pressureregulation of the fluid in fins 12 is not required.

In operation, heat exchange pipes 11 are connected to the desired supplyand discharge conduits of the system with which heat exchanger 10 is tobe used. For example, if heat exchanger 10 comprises the condenser of arefrigeration system, one end of heat exchange pipes 11 would beconnected with the discharge line of a compressor (not shown) and theother end of heat exchange tube 11 would be connected with the expansiondevice (not shown) of the refrigeration system. The hot fluid such asrefrigerant gas which is to be cooled or condensed flows through theinterior of heat exchange pipes 11. A volatile liquid refrigerant suchas water is introduced into the interior 16 of fins 12 by means ofheader 17. Since the walls 13 and 14 of fins 12 are porous, the volatileliquid is enabled to seep by capillary action through the walls where itmay be evaporated from their exterior surface. As used herein, the termporous refers to the characteristic of a body having a large number ofsmall internal pores or voids which communicate with each other and withthe surface of the body.

When in use, heat is conducted from a fluid in pipes 11 through thewalls of the pipes to the Walls 13 and 14 of fins 12. Since the materialof pipes 11 and fins 12 is preferably a relatively good heat conductor,a relatively low resistance thermal path is established to dissipateheat from pipes 11. Heat reaching the surface of fins 12 is absorbed bythe film of water or other volatile liquid on the surface of the finsand the liquid vaporizes. The vapor then escapes into the ambientatmosphere carrying with it the latent heat of vaporization of theliquid which was removed from the fluid in pipes 11. As the volatileliquid heat exchange medium is vaporized from the exterior of fins 12,additional liquid is supplied to the exterior surface of the fins bycapillary action from the interior 16 thereof. Therefore, substantiallythe entire exterior surfaces of fins 12 are continuously supplied with athin film of the liquid heat exchange medium which is available forvaporization therefrom.

Heat exchanger 10 may be suitably manufactured by compacting and rollinga powdered metal such as copper having relatively high thermalconductivity. In order to provide rig'dity to the sheet of compactedmetal, it is desirable that the sheet be sintered. However, care must betaken not to carry the sintering operation so far that the internalvoids in the metal are sealed off from communication with each other orwith the surface, or entirely eliminated by this operation.

The sheet of compacted metal may be then positioned in a hydraulic punchpress where walls 13 or 14 of fins 12 are shaped and trimmed. As hasbeen previously described, it is desirable that walls 13 and 14 beidentical with each. other and merely reversed in respect to each otherto form fin 12. and 14 are formed in the punch press, apertures 23 maybe formed for the accommodation of pipes 11. Walls 13 and 14 are thenassembled on pipes 11 either by first positioning the walls of fins 12in a nesting die and thereafter inserting pipes 11 through apertures 23or by 10- cating pipes 11 in position and sliding walls 13 and 14 offins 12 over the pipes. In either event, walls 13 and 14 are positionedto such that the lip portions thereof face in alternate directions sothat pairs of the lips are relatively closed adjacent each other andwhen subsequently sealed, they will form a hollow envelope shaped fin12.

In order to facilitate the sealing of lips 15 and to facilitate thecreation of a good low resistance thermal bond 'between pipes 11 andfins 12, it is desirable to tin the surfaces which will be joined toeach other with solder. For example, pipe 11 may desirably be a coppertube having a tinned surface and the mating surface of lips 15 may becleaned and fluxed in an acid bath and thereafter tinned. The assemblyof pipes 11 and faces 13 and 14 after being properly tinned may beinserted into a brazing oven 35 which will melt the liquid solder attheir contacting surfaces and upon cooling, a rigid and sealed assemblyis thereby provided. Alternatively, the assembled sides and pipes may besalt bath brazed to accomplish a similar result. Since lips 15 of faces13 and 14 are relatively closely adjacent each other in comparison withthe distance between lips 15 of adjacent fins 12, another means ofsealing edges 31, 32 and 33' would be to dip the edge portions of thefins into a molten bath of solder or plastic and allowing the moltenmaterial which accumu- At the same time that walls 13 will lates betweenlips to cool thereby sealing the appropriate edges of fins 12. In eachof the described alternatives, it will be noted that liquid material ispermitted to solidify between adjacent lips 15 of the sides of fin 12 toform a liquid type enclosure or envelope.

While it is not necessary to do so, it is convenient to space each ofsides 13 and 14 the same distance apart on pipe 11 and construct lips 15of an appropriate size so that when the sides are assembled on pipe 11with the lips placed in alternating directions along the tube, thatpairs of the lips are relatively closely adjacent or in contact witheach other. If the fins are relatively thin, this construction willaccommodate a large number of fins per unit length of pipe and give asubstantial heat transfer surface. If desired, however, the fins may beeither thicker or thinner than the space in between them on pipe 11. Itwill be understood that the relative sizes of fins 12 and heat exchangepipes 11 have been exaggerated in the drawings for purposes ofillustration and that in actual practice the fins may be much narrowerthan shown in the drawings.

The construction illustrated possesses a number of advantages of priorart heat exchangers. For example, since all spray systems and open sumpscan be eliminated by this construction, a heat exchanger of the typedescribed may be located inside a building where the elimination ofentrained moisture might otherwise become a problem. Furthermore,because of the principle of a completely closed heat exchangerconstruction, problems encountered with prior art evaporative heatexchangers such as the accumulation of dirt and soot or the build up ofalgae on the surface of the heat exchanger are completely eliminated.

Another advantage of the construction described is the elimination ofthe sump, recirculating pump, and spray system which is frequentlyrequired in prior art heat exchangers. The elimination of these elementsnot only reduces the initial cost of the system but tends to make itmore reliable and less expensive to maintain because of the reduction inassociated system components. In addition, exceptionally fineevaporative heat exchange characteristics are available by use of theconstruction described because substantially the entire surface of theheat exchange fins may be uniformly wetted with a thin film of volatileliquid thereby overcoming the tendency of external sprays to coalesceinto droplets on the surface of the heat exchange tubes and to createregions of thick film and dry regions which unduly limit the capacity ofprior art heat exchangers.

While reference has been specifically made to heat exchangers such asevapora-tive condensers, it should be understood that the principles ofthis invention are applicable to other heat exchangers as well. Ifdesired a heat exchange construction of the type described may be usedas an air conditioning apparatus to humidify, disinfect, or odorize aconditioned area. For example, high humidity or bacteria control may bemaintained in a hospital operating room by placing a heat exchanger ofthis type functioning as an air conditioner in the room without thedanger of entraining moisture in the air. The heat exchanger is thenused to vaporize water or a germicide which is supplied to the interiorof the hollow fins and a hot fluid may be passed through the heatexchange pipes to vaporize the liquid more rapidly. Various otherapplications, embodiments and modifications will occur to those skilledin the art and it is to be understood that this invention is not limitedto the described embodiments but may be otherwise practiced within thescope of the following claims.

I claim:

1. In a refrigeration system, apparatus comprising a hollow rigidrelatively impervious relatively good heat conducting metal pipe havingan exterior surface and an interior surface, means to pass a first fluidmedium in heat exchange relation with one surface of said metal pipe, a

metal heat transfer member secured to the other surface of said pipe andforming a plurality of relatively low resistance thermal bondstherewith, said heat transfer member comprising a relatively good heatconducting porous metal member having a large number of internal poresin communication with each other and with the surfaces of said member,said heat transfer member having a portion thereof between saidrelatively low resistance thermal bonds which is spaced from said othersurface of said impervious metal pipe and forming with said pipe ahollow fluid passage having a porous wall through which a second fluidmedium may pass While being in heat exchange relation with said firstfiuid medium which is in contact with said one surface of said metalpipe, said heat exchange taking place directly through the walls of saidmetal pipe and said porous metal heat transfer member and through saidplurality of relatively low resistance thermal bonds therebetween.

2. An apparatus as defined in claim 1 wherein said hollow fluid passageis defined by said tube and a pair of substantially identical porousheat transfer members made of compacted metal powder, said identicalporous members having lips offset from the body of the member, saidmembers being reversed in orientation with respect to each other on saidpipe so that said lip portions are adjacent each other while said bodyportions are spaced from each other to form said hollow envelope, andmeans retaining said adjacent lip portions in fluid tight engagementwith each other.

3. A condenser for use in a refrigeration system comprising a hollowheat conducting tubular metal member having an exterior surface and animpervious interior surface defining a first fluid passage, means topass a first fluid medium through said first fluid passage in contactwith said impervious inner wall of said tubular memher to promote heatexchange between said first fluid medium and said tubular member, a heatconducting metal heat transfer member disposed on the exterior wall ofsaid tubular metal member, said heat transfer member forming a pluralityof spaced relatively low resistance thermal bonds with the exteriorsurface of said tubular metal member at spaced locations thereon toprovide a plurality of spaced heat conducting paths therebetween, aportion of said heat transfer member intermediate said spaced heatconducting paths being spaced from the exterior Wall of said tubularmetal memher to define a second fluid passage disposed therebetweenhaving a porous metal heat conducting wall, so that a second fluidmedium passes through the porous metal wall of said second fluidpassage, said second fluid medium being in heat exchange relation Withsaid first fluid medium by conduction of heat through said heatconducting paths and through the heat conducting metal of said tubularmember and said heat transfer member, said heat transfer membercomprising a relatively porous metal heat conducting structure having arelatively large number of internal pores communicating with each otherand with the surfaces of said porous structure, so that said secondfluid medium may pass through the pores of said porous heat transfermember while simultaneously exchanging heat with said first fluid mediumand undergoing a change in state.

4. A refrigeration system including a condenser comprising a hollowimpervious heat conducting metal tube having an exterior surface and animpervious interior surface defining a first fluid passage therein, aporous metal heat conducting heat transfer member disposed on theexterior surface of said metal tube, said heat transfer membercomprising a compacted heat conducting metal powder member having arelatively large number of internal pores in communication with eachother and with the surfaces of said member, said porous metal memberhaving portions thereof disposed in heat conducting relation with spacedportions on the exterior surface of said impervious metal tube toestablish spaced heat conduct- '3 a ing bonds therebetween, and saidporous metal memher having another portion thereof between said spacedheat conducting bonds that is spaced from the exterior surface of saidimpervious tube, the portion of said porous metal member spaced from theexterior surface of said impervious metal tube defining with theexterior surface of said tube a second fluid passage, means to pass afirst fluid medium through said first fluid passage defined in saidimpervious metal tube so that said first fluid medium contacts theinterior surface thereof and is enabled to exchange heat therewith,means to pass a second lfluid medium through said portion of the wall ofsaid porous metal member which is spaced from the exterior surface ofsaid impervious metal tube to exchange heat between said second fluidmedium and said porous 15 2,941,759

metal member therebv placing said first and'second fluid mediums in heattransfer relation through said spaced heat conducting bonds, said heatexchange relation being accompanied by a change of state of said secondfluid medium passing through said porous metal mem ber.

References Cited in the file of this patent UNITED STATES PATENTS1,571,438 Schopf Feb. 2, 1926 2,082,756 Pridham June 1, 1937 2,766,597Gieck Oct. 16, 1956 2,838,830 Huggins June 17, 1958 2,914,842 ModineDec. 1, 1959 Rice June 21, 1960 UNITED STATES PATENT OFFICE CERTIFICATEOF CORRECTION Patent N055 3 0503959 August 28, 1962 Donald G, Rich It ishereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 3, line 56 for 0f"" first occurrence read or column 4,, line 55,for "closed" read closely Signed and sealed this 15th day of January1963.,

(SEAL) Attest:

ERNEST w. SWIDER DAVID LADD Attesting Officer Commissioner of Patents

